LADOTD Roundabout Assistance Contract

Transcription

1 LADOTD Roundabout Assistance Contract

2 Services Provided: Preliminary Design Development Quick 2D Layout & Analysis Ballpark Design and Capacity Software Training 2 Days of Design or 2 Days of SIDRA / CAD / VISSIM Peer Review of Designs by Others Based on EDSMs

3 The Real Limitation to the Capacity of a Roundabout is at the Yield Line The availability of usable gaps in the circulatory roadway traffic for approaching vehicles trying to enter the roundabout is what truly limits the roundabouts capacity THE ACTUAL DESIGN SPECS DON T REALLY MATTER AS LONG AS IT IS A GOOD DESIGN

4 Capacity Limits - Not Lane by Lane If sum is 0 1,100 then Single lane works If sum is 1,100 1,400 then Single lane might work If sum is 1,400 1,900 then 2 laner works If sum is1,900 2,300 then 2 laner might work If sum is 2,300 2,900 3 laner might work

5 Quick Capacity Guesstimate LOS A LOS A / B LOS B / C LOS C / D LOS D / E LOS E / F DON T EXCEED 1400 VPH AT THE CONFLICT POINT FOR A 1 LANER

6 Design Steps 1 ST place 150 diameter circle at center of existing intersection. All work being done at this point is with paint lines curb lines are just offsets from the paint lines

7 Design Steps 2 nd copy 150 diameter circle parallel around 18 or so twice once for the travel lane and another time for the truck apron NOTE: later you will need to check with AutoTurn, AutoTrack or a similar program

8 Design Steps 3 rd hatch out the truck apron so it is clear what that area is going to be used for

9 Design Steps 4 th use a 300 to 800 fillet to tie the center line to the exit side of the truck apron and the left edge line to the outside of the roundabout use the same radius to let CAD worry about the taper..

10 Design Steps 5 th copy the new center line over 12 for your new right edge line

11 Design Steps 6 th use a 90 to 110 fillet to tie in the approach. Use the same radius on both sides let CAD take care of the taper

12 RESULT One leg is done you now have an approach with geometry that requires vehicles to slow down before the yield line. This technique has 2 points of speed reduction you have staged and staggered the speed reduction

13 RADIAL This layout technique has only 1 point of speed reduction and it is at the pedestrian and circulating vehicle conflict area. Also, the driver does have a clear view into the roundabout

14 Alterations to Geometric Layout Decrease Exit Radii to avoid R.O.W. Impact Reducing Exit Radii gets you closer and closer to Radial design (+/- 100 radius) Run Tangent Line from Center Line to Increase Splitter Island Length and Width

15 Decrease Exit Radii to avoid R.O.W. Impacts

16 Use Tangent Line For Larger Island Original Layout Shown with 660 exit radius and 100 entry radius

17 Use Tangent Line For Larger Island Tangent line, shown in black, now goes from new center line to point still left of center of roundabout

18 Use Tangent Line For Larger Island The area hatched in blue shows extra width and length of new splitter island still using a 660 exit radius and 100 entry radius

19 Unusual Geometry Example 2 Separate Roundabouts for 190 / 1077 Skewed Intersection

20 Unusual Geometry Example 4 Separate Roundabouts for 190 Causeway Corridor

21 SIDRA / CAD VISSIM TRAINING STEP BY STEP QUICKLY

22 Once you have named your analysis and verified that the layout is correct, the next step is to insert the geometry for the roundabout. ON TO THE ACTUAL INPUTS Usually the geometry hasn t been developed yet so general values are usually used at this point

23 THE INTERSECTION INPUTS This is where you can specify the actual roadway geometry for the intersection the number of legs as well as the orientation of the legs (shown is the basic 4 way N, S, E, & W) The title and subtitle should be clearly defined here so that the output is easily distinguished from other outputs

24 Here is where you name the legs of the roundabout - this example shows Route?? Northbound THE APPROACHES & LANES ARE NEXT

25 THE APPROACHES & LANES ARE NEXT Lanes can be added & deleted just right click by the green arrow and select what you want to do. You can specify turning movements here as well You must remember to add circulating lanes if you add additional thru lanes as in this example we ll cover this a little later

26 THE APPROACHES & LANES ARE NEXT Lane types are also defined here shown here is a right turn slip lane that still yields to exiting traffic You should also define how this lane was developed this example has a 100 long right turn bay developed from the single lane approaching roadway

27 THE ROUNDABOUT GEOMETRY TAB Here is where you set the center island diameter not the roundabout overall diameter. You can right click on any of the values and apply changes to the intersection as well as just that individual leg Here is where the environment factor can be adjusted we ll discuss why later

28 THE ROUNDABOUT GEOMETRY TAB This step is often missed when adding lanes to an approach if you start with a single lane roundabout and add another thru lane for capacity you need to add another circulating lane as well as another exiting lane on the leg from the north. Another reason why it is good to check the layout every now & then

29 STEP 1 PLACE EDGE LINES The easiest way to do this is to just approximate the center line of the approach and then copy parallel your 11 or 12 lane width. You don t need to be exact with the lines, especially very close to the intersection since the fillets will get rid of that part of the approach and exits anyway.

30 STEP 2 PLACE CIRCLE AS DESIRED The actual placement of the center of the circle is important but there isn t an absolute best spot all long as the design principles are followed quite a few center island locations will work just as well as the others There are a few that will definitely be more challenging though

31 STEP 3 COPY THE CIRCLE TWICE Copy the circle twice once for the truck apron and another time for the center island. The actual width of the travel lane and truck apron will be based on vehicle tracking running AutoTurn or AutoTrack isn t part of this course

32 STEP 4 HATCH OUT THE TRUCK APRON This will make it clearer when you start doing the fillets as to which lines go with which other lines. For the VISSIM layout you could make the apron a different color or even pattern as well as the center island but just hatching it for now is fine

33 STEP 5 FILLET THE EXITS The use of larger exit radii will allow for better speed control on the approach to the roundabout. The exit speed is dictated by circulating speed plus acceleration not just measuring the exit radii

34 STEP 6 COPY CENTER LINE FOR THE APPROACH Just do another copy parallel 12 for the right side of the approach Having the approach follow the exit radii is what will dictate the lower approach speeds

35 STEP 7 TRIM THE OLD LINE ON THE APPROACH You can either use the trim command or use the extend 2 elements to intersection command.

36 Fillet the new right edge to the outside edge of the roundabout and trim the center line to the approach side of the truck apron you want to truncate none when doing the center line because you need it for the exit and splitter island. STEP 8 FILLET THE APPROACH

37 STEP 9 TRIM LINES THAT GO INTO ROUNDABOUT Remove the part of the fillet lines that go into the circulatory roadway of the roundabout using the outside edge of the roundabout as the cutting edge.

38 STEP 10 TRIM LINES THAT GO ACROSS EXITS Using the partial delete command you can get rid of any lines that aren t going to appear in the final layout especially the lines across the exits.

39 STEP 11 FILLET ANY SKEWED APPROACHES For this example the only approach that needs a fillet to not look odd is the approach from the SW. I tried a 20 radius.

40 STEP 12 SNAG AN IMAGE FOR VISSIM This concludes the 12 step program for CAD Hopefully this is one of the easier 12 step programs to complete

41 First left click on the link then use the right mouse button to insert moveable points within link to establish roadway geometry. We ll just get it close for the first run quite a bit of time can be spent smoothing out the layout

42 Once you have the layout looking good in one direction you can either draw the other direction or take the easy route and double left click on the roadway to bring up the link data and click Generate Opposite Direction

43 Now all you have to do is revise the layout around the roundabout the approach and exit curvature will already be set Besides seeing the roadway in normal view you can also view the roadway in centerline mode. Hit CONTROL A to change between the views. This will come in handy later

44 You can easily modify the roadway curvature in either view Now it s time to do the side street layout

45 The side street with the center turn lane makes the Generate Opposite Direction technique less of a time savings I usually draw the side street up to the roundabout but not thru the roundabout. We will use connectors to tie everything together. Centerline view helps when doing connectors

46 Connectors tie links together think of them as a way to go from one track to another

47 Once the links are done, connectors must be inserted for right, thru, and left turn movements as of now, no vehicles can turn off of main movements. Do this for all approaches Right clicking and dragging from one link to another will insert connector use # of points to create smooth arc. Connectors will be displayed with black dots, not grey

48 Connectors tie links together think of them as a way to go from one track to another

49 Connectors will show up as pink lines in centerline view it is good to avoid using blue and pink lines when developing a layout in CAD so it doesn t get confusing when looking at VISSIM in centerline mode

50 PEER REVIEWS

51 Most Common Recommendations / Comments from Peer Reviews Need Offset Left Alignment Remove Entry Path Overlap Check / Verify Truck Paths Construction Sequencing / TCP Plans

52 Radial Alignment Allows High Speed Potential

53 Offset Left Alignment Reduces Speed Potential

54 Radial Alignment Allows High Speed Potential

55 Offset Left Alignment Reduces Speed Potential

56 Entry Path Overlap Created by Using Single Lane Design Technique on 2 Laner

57 ENTRY PATH OVERLAP Created by using single lane design techniques on 2 lane roundabouts. There is one critical new step that needs to be added

58 ENTRY PATH OVERLAP Think about the driver. They get to the yield line look left then look straight ahead they forget about the 100 radius that they have just been following

59 Correct 2 lane Approach Layout with Left Offset & Truck Gore Striping

60 Truck Paths Need to be Checked - Rechecked

61 Paths that Need to be Checked Left Approach

62 Paths that Need to be Checked Right Approach

63 Right Turn May Need More Space

64 Construction Sequence TCP Plan

65 Construction Sequence TCP Plan Best Option Close Intersection Next Best Option On Site Detour Typical Sequence Multi Phase Partial Closures

66 Thanks to Everyone Here This Morning and To All that Contributed to this Presentation Enjoy the rest of the conference!